Method of and means for reducing interference in transmission systems



Sept, 2 @2924. 4 H. \N. HITCHCOCK Lfifiiifig HOD DEMAND MEMIS Fon REDUCIING NTERFERENCE IN'TRANSMISSION SYSTEMS v MET Filed Sen. 6, 1 21 I Powerlm i Ruav go who W. HITCH-Z0063, 0Z HEW :ZGRK, N. 5,, ASSIG-NO'R CK AMERICAN TELEPHONE AND TELEGRAFH COMPANYQA CORPQBATION 015' NEW YQBE.

Application filed my application, Serial No. 363,180, iileei Hmoniarch 6i, 1920. It is iiesciibeti with-particular reference to the case in which n telephone n is iiitiuctiveiy influenced by a power line, eppiicshie to many Wideiy vniying of transmission systems suhiect in- Lience.

1e present invention proposes to reduce interfering ener 'y relatively to the use energy hy I an amplification nsei'ni ene the intei'iiemng m y ent rs path oi transmission and es With ihe useful energy, this eecompiished in pei'ticuiaz' ease herein to by the use oi" amplifying elements associated with the transmission hue oints substantially outside the zone in the power line paraheis the t-eiep ione yin-g ievices ate en oneness miles of input to o the (Z11 ecton of how of en traversing the same, so that the termecnste point to one ten: 31113.18 oi the line reduced relatively to usef'i energy which traverses she "n terminni to terminal.

W ereas in parent s piics'tion, of which is :1 co "nustion, i. orioeti and claimed specifieaiiy the case in which the ratio of output input was ieiger than unity for the enn'ent flowing towards the zone interference and hes then unity for current flowing-from the zone of interference to the --'zerznineis in .is eppiieetion E deseiihs specincaiiy the case in which the msio gresier i'zhen unity for currents fies-ling in hogh direc ions but in which the ratio for cements flowing to the zone of iniesierence is greater thanfoi' cori'eni's flowing from the zone of inteiffercnce.

September 6, 1921.

IHQL) OF AND MEANS FOR REDUCING IENTERFERENCE IN TRAIKSEZISSION S..$TE2"$.

Eerial IEO.

A good ui'ideistsnding of the invention may now he had A one the foiiowing description of certain methods practicing, and of certain forms and. 1 'sngeinents of apparatus anti circuit oi embodying the some reference being had to the accompanying (ii-o. wing, in which Figure l iiiustrates in (iiagmmimztic View one form of circuits embodying the inven'eion; 2 and 3, curves showing graphically the distribution of currents in the iine conductors that wouid be Without' the application of my invention; Figs. i and 5, curves simiier to 2 and showing the effect of of E 1 the eppiic tion of the methods anti means of s? r m t se Wi w s. ng between stations in n l ion eppiying our rent to, and responding to ewi'ent in, the eondoc'iors of L haze. le /ices for snite oi. sinipiiciby snows in conventional 1', may he oieiinai'y suhseribers one sets comprising transmitters and ieceiveirs or any other suitable s gnaling ep- Line T is persiieied through a disioy a power line which eonsequentiy inthices in iine 'i a disturbing current Which it is the object of the present invention to i reintiveiy to the nseini or voice current. epeeters R and are associated Wain hne i intermediate the region and. i.

L These repeaters a e provided for attaining the objects of this invention sn'ci their organization is &escribeti h explain the manner in which I bring shoot the attenuation of the disturbing cur rent i'eiutiveiy to the iisefui current, I shall first describe ihe conditions which would be obtained if the re 'ieulers R and H were removed from the awe. let ordinate a in Fig. 2 designate the smpmlude of voice current applied to iine hy the i'i'zinsiuitting eiement oi the device i. Due to Liissi} Voice energy by the iine, this current (leition A to station 5 (3,- so thni the current ceiving element of the i i sented e the om inate 7). the

z'otiveiy small or if he ierminais of the line.

amplitude a the ettenuatlon a storms is large the amplitude 6 will be too small for satisfactory conversation and amplification would be desirable. Let the ordinate d in Fig. 3 denote the amplitude of the current induced in line '1 by the powerline in the region Di, this current having been drawn for sake of clearness to a disproportionately large scale for the ordinary actual case. This current flows towards the terminals A. and ll and, as indicated by the curve denoted f, it is gradually attenuated by the line so that when the current reaches the receiving element at stations A and B, the amplitude of the disturbance is as shown by the ordinates g and h, respectively. It will be observed that under the assumed conditions the amplitude of the disturbance is very large at station E compared to that of the voice current, showing that there is serious interference. If the frequency of the disturbance is within the audible range, the line is very noisy, making it extremely difiicult to understand the received speech. Conditions are equally poor at station A for thereason that the voice energy applied to the line by the transmitting element of the device 2 is attenuated substantially plike that of the transmitter at station A.

The repeaters R, and R serve to reduce the relative loudness of the disturbance. The former of these is located between "station A and the region otdisturbance and the latter between station B and the said region: Each repeater consists of a pair of networks N, shown conventionally, "for balancing the sections of line with which they are associated, and also includes a pair of three winding transformers M, which serve to associate the devices 2' and 4 with the line conductors. These devices comprise amplitying elements, herein shown as electron tubes. The circuit arrangements for associating these are now well understood in the art. In this invention, however, I in clude as an element of each side of the re peater means for controlling the amplifyingfaetor of each tube. In this case this means consists of a resistance r, shunted across the secondary of the input transformer of the device 3 and constituting, by

means of a variable contact, a potentiometer to control the voltage impressed on the input terminals of the element 3. A similar potentiometer arrangement is provided for the element t and for the purpose of this invention, the potentiometer of Fig. 4 would be adjusted for a lower amplifying factor than that oi the element 3. The potentiometer might equally well be put across the primary of the transformers.

As thus described, the repeaters R, and R constitute the well-known two-way twoelement or 22-type repeater. By virtue of the above described arrangements, R, serves to amplify currents traversing the same from east to west with one factor of amplification and to amplify currents in the opposite direction with a. smaller factor of amlification, whereas R amplifies currents irom east to west with a large factor and amplifies those 'from west to east with a small factor. This is illustrated in 4, wherein a again represents the amplitude of the voice currents applied at station A toline T. When this current reaches the repeater B, it has been attenuated to a value '9 in accordance with the attenuation curve 0' of Fig. 2. The repeater R, amplifies the current to a value indicated by the ordinate 1-", the ratio of amplification being assumed in this case as 4 to l. As'this current flows toward B, it is attenuated by the line, so that at B, it has a value represented by the ordinate m. The repeater R serves to amplify the current to a value indicated by n, so that the current which is impressed on the receiving element at station B is of about the normal value requiredfor satisfactory service at such a station' This is not true, however, of the energy of the disturbance, as illustrated by Fig. 0. The induced current flows from the region D towards the terminals of the line with normal attenuation, so that the amplitude thereof is as indicated by "the ordinates '2, when the currents reach the repeaters d, and R These repeaters serve to amplify these disturbances .also, as shown by ordinates 1 but in no greater ratio than for thevoice current. As a result. my invention serves to reduce the noise on the line but gives the useful or voice current a value satisfactory for telephone communication.

The extent of the reduction of the noise depends on the relative value of the ratio of the two amplifiers at each repeater station. If this ratio is doubled, the noise is reduced accordingly and if the ratio is decreased, the relative noise is accordingly increased. The correct ratio in any particular case depends,

of course, on the frequency and intensity of the noise, the maximum allo rable amount of interfernece, and on certain. commercial considerations as to cost, as will, be readily understood by those fan'iiliar with the art. As an example illustrating the application of the invention, each repeater may be arranged to amplify 4 to 1 for currents flowing to wards the zone of interference and 2 to 1 for currents flowing from the zone of interference. In this case, the total amplification of the voice current from station A to station E is roughly, 8 to 1, whereas that of the noise is but 2 to 1. In other words, although the noise is doubled in loudness, the volume of the voice is increased eightfold over what it would have been had there been no repeaters.

The repeaters thus serve to bring about an amplification of the voice current, as well as to suppress the noise relatively to the voice. 

